Add support for .cargo/config.toml

[LuckyTurtleDev]

cargo-msrv ignores the .cargo/config.toml. And does still try to use the default target.
A workaround is to manual set the target with --target thumbv7em-none-eabihf

[target.thumbv7em-none-eabihf]
runner = "hf2 elf"
#runner = 'probe-run --chip ATSAMD51J19A'

[build]
target = "thumbv7em-none-eabihf"
rustflags = [

  # This is needed if your flash or ram addresses are not aligned to 0x10000 in memory.x
  # See https://github.com/rust-embedded/cortex-m-quickstart/pull/95
  "-C", "link-arg=--nmagic",

  "-C", "link-arg=-Tlink.x",
]

[foresterre]

Ai, you've discovered a feature we do not support yet. I do hope to add support for Cargo's config file at some point.

[rursprung]

with the target support now fixed (cf #825) i think support for build.target in .cargo/config is the last missing piece of the puzzle to ensure that cargo-msrv works out of the box and with no additional manual switches for most embedded projects. though admittedly specifying the target manually is low overhead (once you know that you need to do it).

[foresterre]

There's also a bit of luck on another front, someelse already did the hard work of parsing the config.toml 😄: https://crates.io/crates/cargo-config2. Well that will save some work!